Linear motion variable resistor with transverse fine adjustment

ABSTRACT

An actuator is movable along the edges of parallel resistance and collector strips mounted in a case. The resistance strip is provided near each end with a transverse notch. Bridging contact means carried by the actuator engage both strips. Movably mounted in the actuator is an adjusting member that has an inner end connected with the contact means and that can be moved lengthwise to move the contact means forward and backward beside the strip notches to vary the distance from the point of engagement of the contact means with the resistance strip to the reduced areas of the resistance strip at the inner ends of the notches for fine adjustment of the resistor.

United States Patent Bang -451 Mar. 7, 1972 Mogens W. Bang, Ridgway, Pa.

[72] Inventor:

[73] Assignee: Stackpole Carbon Company, St. Marys,

[22] Filed: Mar. 8, 1971 [21] Appl. No.: 121,896

[52] U.S. Cl .338/122, 338/181 [51] Int. Cl ..Il0lc 9/02 [58] FieldofSearch ..338/118, 122, 160, 176,180, BIBS/181,183,195

[56] References Cited UNITED STATES PATENTS 3,551,871 12/1970 Eberwern..328/122 1,652,017 12/1927 Krauss ..338/l81 X Primary Examiner-Lewis H.Myers Assistant Examiner-Gerald P. Tolin Attorney-Brown, Murray, Flick &Peckham [5 7] ABSTRACT An actuator is movable along the edges ofparallel resistance and collector strips mounted in a case. Theresistance strip is provided near each end with a transverse notch.Bridging contact means, carried by the actuator engage both strips.Movably mounted in the actuator is an adjusting member that has an innerend connected with the contact means and that can be moved lengthwise tomove the contact means forward and backward beside the strip notches tovary the distance from the point of engagement of the contact means withthe resistance strip to the reduced areas of the resistance strip at theinner ends of the notches for fine adjustment of the resistor.

5 Claims, 3 Drawing Figures LINEAR MOTION VARIABLE RESISTOR WITHTRANSVERSE FINE ADJUSTMENT Linear motion variable resistors, such asPotentiometers, are well known and are provided with actuators or slidesthat move contacts along resistance elements, In some cases it isdesirable to be able to make finer adjustments than can be accomplishedconveniently by normal movement of the actuators. It is therefore amongthe objects of this invention to provide a linear motion variableresistor in which both coarse and fine adjustments can be made byseparate adjustments, and in which fine adjustments can be made quicklyand easily after any coarse adjustment.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which FIG. 1 is a side view of a potentiometenwith part of it broken away;

FIG. 2is an enlarged fragmentary longitudinal section taken on the lineIIII of FIG. 1; and

FIG. 3 is a cross section taken on the line IIIIII of FIG. 2.

Referring to thedrawings, the long rectangular case 1 of a variableresistor, such as a rheostat or potentiometer, may be formed from amolded plastic orother suitable rigid material. The case preferably ismade from two molded half-sections that have meeting edges extendingfrom front to back across the end walls of the case and lengthwise alongits back or base. The half-sections are joined tightly together in anysuitable manner.

Inside the case a metal collector strip 2 and an electrical resistancestrip 3 are mounted at the opposite sides and are parallel. Thecollector strip is provided with an integral terminal 4 that extendsthrough the back of the case, while each end of the resistance strip isconnected to a metal terminal 5 likewise extending through the back.

Between the two strips there is a bridging contact member that engagesboth of them. This contact member can be moved lengthwise of the stripsby an actuator that is movable along the front edges of the strips. Forexample, the actuator may be a slide 7 that is slidably mounted in acentral slot 8 extending lengthwise of the casein its front or top. Theslide has laterally opening grooves 9 in its opposite sides receivingthe side walls of the slot to hold and guide the slide. The ends of theouter sides of the slide may be provided with projections I for manuallymoving the slide lengthwise back and forth along the slot.

It is a feature of this invention that the bridging contact member isnot secured in fixed position to the actuator or slide, but isadjustable forward and backward relative to it. Accordingly, the contactmember is carried by a small block 12 movable in an open frame l3projecting rearwardly from the slide and across the two strips in thespace between them. The plane of the frame is parallel to the strips,and the frame is spaced from them. The block engages the parallel sidesof the frame and, as shown in FIG. 3, is provided with a central passagel4 extending through it at right angles to the strips. Disposed in thispassage is the bridging contact member, which may take the form of apair of spaced contact slugs l urged apartby a coil spring 16 betweenthem. The slugs project from the opposite sides of the block intoengagement with the two strips.

The central portion of the slide is provided with an opening through it,in which an adjusting member is mounted for longitudinal movement. Theinner end of this member is connected with block 12. Preferably, theadjusting member is a screw 18 threaded in the slide, with its inner endrotatably mounted in the front portion of the block and retained in it.The outer end of the screw is provided with means, such as a knob 19,for turning it so that the screw can be screwed inwardly or outwardly toadjust'the block across the two strips. Such transverse adjustment ofthe bridging contact means would not, with the usual resistance strip,affect the adjustment of the resistor. However, since it is intendedthat turning the knob shall affect the electrical resistance of theunit, the resistance strip is provided near each end with a notch 21that extends part way across it. The notches may extend from either.edge of the strip. For best results, they extend more than halfwayacross the strip so that the areas of the resistance strip at the innerends of the notches are less than half as wide as the rest of the strip.

When the bridging contact member is moved forward or backward beside thenotches, the distance from the point of engagement of the contact memberwith the resistance strip to the reduced area of the resistance strip atthe inner ends of the notches will be changed. Thus, regardless of thelocation of the contact member along the resistance strip when thecontact member is at the back of the strip, it will engage the stripfarther from the front or inner ends of the notches than if the contactwere directly opposite those ends, so a longer resistance path will beprovided. This is illustrated in FIG. I by the two broken lines A and B.Assuming that the contact member engages the resistance strip first atthe right-hand end of line A and then at the right-hand end of line B,it will be seen that the distance from the first point to the left-handend of lines A and B is less than from the second point, because line Ais shorter than line B. There is a similar variation in distancesbetween the contact member and the inner end of the other notch.

It will be realized that even though the contact member is moved all theway from its front position to its rear position after the slide hasbeen moved along the case toa desired locathe screw permits extremelyfine adjustments of the electrical,

resistance to be made quickly and easily after the slide has been movedalong the case to an approximately correct position.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

Iclaim:

l. A linear motion variable resistor comprising an elongated case,parallel resistance and collector strips mounted therein at its oppositesides and extending lengthwise thereof, said strips having front andrear edges, the resistance strip being provided near each end with atransverse notch reducing the width of that strip at that location, anactuator movable lengthwise along the strips at their front edges,bridging contact means engaging the strips and carried by the actuatorfor movement thereby lengthwise of the strips, said contact means beingmovable forwardly and rearwardly in the case, and an adjusting membermovably mounted in the actuator and projecting from its front and back,said member having an inner end connected with said contact means, andthe adjusting member being adapted to be moved transversely of saidstrips in order to adjust the bridging contact means forward andbackward beside said notches, whereby to vary the distance from thepoint of engagement of the contact means with the resistance strip tothe reduced areas of the resistance strip at the inner ends of saidnotches for fine adjustment of the resistor.

2. A linear motion variable resistor according to claim 1, in which saidnotches extend more than halfway across the resistance strip.

3. A linear motion variable resistor according to claim I, including anopen frame projecting rearwardly from the actuator between the strips ina plane parallel thereto, said contact means being slidably mounted insaid frame.

4. A linear motion variable resistor according to claim I, in which saidadjusting member is a screw threaded in the actuator and having itsinner end rotatably connected with said contact means.

5. A linear motion variable resistor according to claim 4, including anopen frame projecting rearwardly from the actuator between the strips ina plane parallel thereto, and said contact means including a block and abridging contact member carried by the block, the block being slidablymounted in said 5 frame, and the inner end of i said screw beingrotatably mounted in the block and secured thereto.

1. A linear motion variable resistor comprising an elongated case,parallel resistance and collector strips mounted therein at its oppositesides and extending lengthwise thereof, said strips having front andrear edges, the resistance strip being provided near each end with atRansverse notch reducing the width of that strip at that location, anactuator movable lengthwise along the strips at their front edges,bridging contact means engaging the strips and carried by the actuatorfor movement thereby lengthwise of the strips, said contact means beingmovable forwardly and rearwardly in the case, and an adjusting membermovably mounted in the actuator and projecting from its front and back,said member having an inner end connected with said contact means, andthe adjusting member being adapted to be moved transversely of saidstrips in order to adjust the bridging contact means forward andbackward beside said notches, whereby to vary the distance from thepoint of engagement of the contact means with the resistance strip tothe reduced areas of the resistance strip at the inner ends of saidnotches for fine adjustment of the resistor.
 2. A linear motion variableresistor according to claim 1, in which said notches extend more thanhalfway across the resistance strip.
 3. A linear motion variableresistor according to claim 1, including an open frame projectingrearwardly from the actuator between the strips in a plane parallelthereto, said contact means being slidably mounted in said frame.
 4. Alinear motion variable resistor according to claim 1, in which saidadjusting member is a screw threaded in the actuator and having itsinner end rotatably connected with said contact means.
 5. A linearmotion variable resistor according to claim 4, including an open frameprojecting rearwardly from the actuator between the strips in a planeparallel thereto, and said contact means including a block and abridging contact member carried by the block, the block being slidablymounted in said frame, and the inner end of said screw being rotatablymounted in the block and secured thereto.